Safety syringe mechanisms are known wherein the syringe is initially held fully within a housing and, after injection, the syringe is again drawn back into the housing. Such arrangements usually have a drive member which can be released and driven forward, firstly to cause the needle at least of the syringe to project from the housing, and then to cause a dose to be ejected from the syringe through the enclosed needle. At the end of the injection procedure, the syringe is caused to be withdrawn again into the housing by a return mechanism. This invention aims to provide a syringe firing mechanism of this nature which is relatively simple in construction and which can readily be operated to perform the two stages of exposing the needle of the syringe and withdrawing the syringe into a housing after injection.